This invention relates to a respiration assistor for use in a breathing system. The invention has been developed primarily for use in conjunction with anaesthesia breathing systems and the invention is herein described in that context. However, it will be understood that the invention does have broader application, for example for use in conjunction with breathing systems that are employed in intensive care and high dependency hospital environments for weaning patients off ventilators and alleviating respiratory insufficiencies.
A typical anaesthesia breathing system, when reduced to its essential elements, comprises an inspiratory limb, an expiratory limb, a Y-piece joining the two limbs at the patient side of the system, and a T-junction joining the two limbs at the so-called bag side of the system. A reservoir bag (also known as a rebreathing bag) is connected to the T-junction and, in a semi-closed circuit system, a CO2 absorber is connected in circuit with the inspiratory limb at the bag side of the system. An inspiratory valve is located in the inspiratory limb, between the CO2 absorber and the Y-piece in the case of the semi-closed system, and a fresh gas inflow connection is provided between the CO2 absorber and the inspiratory valve. An expiratory valve is located in the expiratory limb, between the Y-piece and the T-junction, and an adjustable pressure limiting (APL) valve is located in the expiratory limb between the expiratory valve and the T-junction for the purpose of venting excess gas from the system.
Monitoring of expired gases for CO2 has been adopted widely in recent times and, as a result, it has become more evident that some patients who breathe spontaneously during anaesthesia tend to underventilate. As a consequence, the patients manifest a higher-than-desirable end-expiratory CO2 level, and this has been observed particularly in older patients for whom the SpO2 level may be considered satisfactory but for whom the EtCO2 readings have been observed to rise to levels that indicate the need for ventilatory assistance. This assistance may be provided by squeezing the reservoir bag intermittently to produce positive pressure respiration or, if synchronised with the patient""s inspiratory efforts, to provide periodic manual assistance.
However, using the reservoir bag to provide manual assistance is inconvenient for an anaesthetist. It intrudes upon other demanding activities, and creates a need to readjust the APL valve and to xe2x80x9cchasexe2x80x9d continually the ventilatory parameters.
The present invention is directed to an apparatus which is intended to be used to provide respiratory assistance for patients who breathe spontaneously during anaesthesia, so that the end-expired CO2 level will be maintained at or near the normal physiological level.
Broadly defined, the present invention provides a respiration assistor for use in a breathing system and which comprises:
a) a gas supply passage,
b) a gas flow detector located in the gas supply passage and arranged to detect through flow of inspired gas,
c) an electrically activatable pressure booster connected in circuit with the gas supply passage, the pressure booster being of a type through which inspired gas may be drawn independently of electrical activation of the pressure booster,
d) a gas delivery conduit for delivering pressurised gas to a patient from the pressure booster,
e) an electrically actuatable expiratory valve,
f) a gas exhaust conduit for carrying expired gas from the patient to the expiratory valve,
g) means for connecting a gas supply in circuit with the gas supply passage, and
h) an electrical control circuit arranged to
i. effect activation of the pressure booster and closure of the expiratory valve upon detection of inspired gas flow through the gas flow detector, and
ii. effect deactivation of the pressure booster and opening of the expiratory valve in the absence of inspired gas flow through the gas flow detector.
The gas supply to which the respiration assistor is in use connected will normally comprise a circuit that includes a flow activated expiratory valve, a pressure relief (excess gas release) valve, a reservoir bag, a CO2 absorber (in the case of a semi-closed system), a fresh gas inlet connection and a flow activated inspiratory valve. With this circuit connected between the electrically actuatable expiratory valve and the gas flow detector, inspiratory breathing of a patient will result in gas being drawn through the inspiratory valve and the gas flow detector. The pressure booster will then be activated and the electrically actuated expiratory valve will be closed, resulting in slight pressurisation of the patient circuit and assisted inflation of the patient""s lungs. Continuing operation of the pressure booster will result in continuing suction of gas through the inspiratory valve and the gas flow detector until the lungs reach full capacity. On reaching full lung capacity, inspiration ceases, the inspiratory valve closes and normal expiration commences. When this condition is sensed by the gas flow detector, the pressure booster is deactivated and the electrically actuatable expiratory valve is opened, so that normal lung deflation and gas expiration may continue.
An important feature of the invention is that respiration assistance is provided at the patient side of the complete breathing system without interfering with system components that normally are provided at the bag side of the system. This means that a reservoir bag may be used in conjunction with the respiration assistor, this in turn meeting the needs of practising anaesthetists.
The pressure booster preferably comprises a blower that is connected in series with the gas flow detector, and the respiratory assistor is hereinafter described as having a pressure booster in the form of a blower.
The blower is selected and energised to assist inflation of the lungs but without interfering with spontaneous respiration by the patient. The blower preferably is driven by an electric motor and the motor may be energised in one of two ways for the purpose of activating the blower. That is, the motor may be energised periodically to provide the required blower drive or the motor may be energised permanently and be connected periodically to the blower by way of an electromagnetic coupling or the like. In either case, the blower will be disconnectable from the electric motor to enable sterilisation of the gas circuit components of the respiration assistor.
The gas flow detector preferably is integrated with an inspiratory valve and, in such case, the flow activated inspiratory valve might be omitted from the gas supply circuit. Alternatively, two inspiratory valves might be connected in series, with one in the respiration assistor integrating the gas flow detector,